The present invention concerns a distributed data processing system--that is, two or more data processing systems which are capable of functioning independently but which are so coupled as to send and receive messages to and from one another.
A Local Area Network (LAN) is an example of a distributed data processing system. A typical LAN comprises a number of autonomous data processing "cells", each comprising at least a processor and memory. Each cell is capable of conducting data processing operations independently. In addition, each cell is coupled (by appropriate means such as a twisted wire pair, coaxial cable, fiber optic cable, etc.) to a network of other cells which may be, for example, a loop, star, tree, etc., depending upon the design considerations.
As mentioned above, the present invention finds utility in such a distributed data processing system, since there is a need in such a system for the processes which are executing or to be executed in the individual cells to share data and to communicate data among themselves.
Information may be thought of as being stored in the form of files in one or more "file systems". A file system is a way of logically organizing data, and it may comprise one or more physical data storage devices. Usually, a file system comprises an organized arrangement of data and a file index identifying the data, its location, and perhaps other characteristics.
In the present invention, any of the individual cells of a LAN may contain one or more file systems. Certain file systems may be unique, while other file systems may be copies in order to provide a degree of redundancy.
There is an urgent need in certain distributed data processing systems to provide "data access transparency". Data access transparency is defined herein to mean that any file can be accessed by any process located anywhere in the distributed data processing system.
There is also an urgent need regarding certain of such distributed data processing systems to provide "data residence transparency". Data residence transparency is defined herein to mean that any file can be accessed wherever it may reside, even if it has been physically moved within the system.